An environmental assessment of green gases production routes: biogas-to-biomethane vs biogas-to-hydrogen

To meet the 1.5°C global warming limit, net-zero emissions targets have been set all over the world. In this context, two green gases, i.e., biomethane and hydrogen, are of utmost relevance. Biomethane is generally obtained through the upgrading of biogas produced by anaerobic digestion. It represents a renewable alternative to natural gas and has several applications in sectors such as transport and energy. Similarly, hydrogen is a key element for decarbonising the global economy. It has applications in sectors such as energy, transport, and construction. Most hydrogen is produced from non-renewable sources generating significant emissions. Therefore, finding alternatives to produce low-carbon hydrogen is an urgent challenge. Although the “green hydrogen” route (i.e., electrolysis fuelled by electricity from renewable sources) is very promising from an environmental perspective, its high electricity consumption represents a barrier to its large-scale implementation. In this regard, the so-called “steam biogas reforming” route represents a viable alternative. It consists of producing hydrogen from biogas obtained from anaerobic digestion. Hydrogen production from biogas replaces the production of biomethane. To this concern, this paper aims to identify the best green gas production route among biogas-to- biomethane and biogas-to-hydrogen from an environmental point of view. Consistent with this purpose, an analytical model was developed to assess each alternative based on the direct, indirect, and avoided emissions. The results showed that the decarbonisation of the green gas production routes and the environmental convenience of either alternative is strongly affected by multiple aspects related to the energetic assets of the country considered.